Foraminiferal sandy contourite of the Limpopo Corridor (Mozambique margin): Facies characterization and paleoceanographic record

Abstract

Contourites encompass a wide variety of sedimentary facies. Some of them show common facies with others deep-water deposits, such as turbidites and hemipelagites. Sedimentological characterization at macro- and microscales is valuable to discriminate those close facies but the distinction is not always clear. Contourites are increasingly used in paleoceanographic and paleoclimatic reconstructions. Improving their characterization is therefore essential to their interpretations.This study aims at characterizing a foraminiferal sandy contourite facies from a sediment core collected on top of a contourite drift under the influence of the Antarctic Intermediate Water/North Atlantic Deep-Water interface located in the Limpopo Corridor (Mozambique margin, Indian Ocean) at 2000 m depth. This work is based on a detailed analysis of the sedimentary record using physical properties (gamma density and magnetic susceptibility) as well as laser grain size and X-Ray Fluorescence core scanning data.Our results show that: (1) the foraminiferal sand is vertically continuous and homogenous over 633 kyr with an average sedimentation rate of 0.26 cm.kyr−1; (2) this contourite facies results from sedimentation with low terrigenous inputs under stable hydrodynamic conditions over time, with relatively strong bottom currents for this water depth (∼16 cm.s−1); (3) during glacial stages, sedimentation rates are lower and bottom current speed is higher than during interglacial stages. We also propose the concept of “Contourite Graphical Chart” which summaries the theoretical distribution of contourite endmembers from cross-plot of “sorting versus grain-size median D50” and their related sedimentary processes.This study highlights the relevance of condensed foraminiferal sandy contourites as long time-scale paleoceanographic archives and provides new insights for studies related to paleoclimatology and paleoecology.